Carbon-nutrient economy of the rhizosphere: improving biogeochemical prediction and scaling feedbacks from ecosystem to regional scales


Joshua Fisher (NASA), Richard Phillips (Indiana University), Edward R. Brzostek (West Virginia University), & Tom P. Evans (INdiana University)

Ecosystems are the primary mechanism by which the Earth removes fossil-fuel derived CO2 from the atmosphere. Nonetheless, as most gardeners and farmers know very well, the ability of plants to grow—and take up CO2—is typically limited by the amount of nutrients (i.e., nitrogen, phosphorus) available to plants. As one walks through a forest, unseen to us is a vast underground network of fungi that operates in a complex economy, whereby fungi scavenge for nutrients and trade them to trees in exchange for sugars. This helps the plants alleviate some of that nutrient deficiency; but, at the same time, the plants lose carbon that they could have otherwise used for growth. The amount of carbon required to “pay” the fungi for a given amount of nitrogen or phosphorus varies from fungi to fungi. Hence, this carbon-nutrient economy is complex with large implications on how ecosystems may or may not be able to soak up CO2 now and into the future.

Projections of the state of the Earth derive from Earth System Models, which formulate Earth processes into myriad mathematical equations run on powerful supercomputers. If processes are missing or the equations are wrong, then this may lead to error in the projections. Currently, these models have not yet included the plant-fungi nutrient economy, primarily because we have not had the key measurements upon which to construct the mathematical equations, until now. Our science team has developed cutting-edge techniques to measure the carbon and nutrient flows between the soil and plants, mediated through plants and fungi, thus enabling the advancement of the modeling of the Earth System. Our project will add this nutrient economy to the models, resulting in significant advances of Earth System Models and understanding of how plants, fungi, and their carbon-nutrients feedback to one another, and to the Earth System as a whole.

The key science questions we seek to address, focusing primarily on temperate forests, include:

  • How do belowground processes affect the spatial and temporal patterns of forest C sequestration, C–N–P cycling, and vegetation response?
  • How does the C cost for plant N and P acquisition control productivity and vary between sites/regions with high versus low nutrient quality?
  • To what degree does inclusion of mycorrhizae increase the ability of Earth System Models to predict land–atmosphere C fluxes across spatial and temporal scales?


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